The prior art is replete with descriptions of ink dispensing rolls with ink metering features. U.S. Pat. No. 4,458,399 issued July 10, 1984 to Kessler describes the use of a horizontally mounted roll comprised of plurality of coaxially mounted, spaced discs positioned within and press fitted against a perforated tube about which a sleeve of porous material is fitted. The spaced discs define a plurality of chambers which hold ink and permit the flow of ink through the perforations of the tube and into the sleeve. U.S. Pat. No. 4,399,751 issued Aug. 23, 1983 to Kessler discloses still another ink dispensing roller having a plurality of axially aligned thin discs wherein each disc has a series of circumferential grooves and axial grooves. The discs are covered by a porous sleeve. Ostensibly, ink flows from the axial grooves to the circumferential grooves and then to the flexible material. Neither U.S. Pat. No. 4,458,399 nor U.S. Pat. No. 4,399,751 describe how the printing rolls are charged with ink.
Another U.S. Pat. No. 3,738,269 issued June 12, 1973 to Wagner describes the structure of a horizontal roller having a porous sleeve of ink-absorbing material with one or more reservoirs of ink within the sleeve. The reservoirs being free of vents to the atmosphere are stated to provide uniform inking.
Industries such as those handling unitary objects and consumer products, e.g., material handling industries, have been converting to various types of bar codes readable by scanning devices. Such devices permit the high speed passage of objects to which bar codes are appended, thus facilitating warehousing and inventory control. A major problem, however, has been the inability of prior printing devices to print the sharp bar code images on objects as they pass by a printer. Most prior art printers use dye based ink which tend to wick or feather, particularly on corrugated boxes, leaving printed codes very difficult or impossible to read by scanners.
Substituting pigment-based ink, a superior ink for quality printing even on the most difficult surfaces, has not proven to be viable since such inks are difficult to uniformily meter and transfer. The pigment-based inks having small particles of pigment suspended or emulsified in liquid as opposed to being in solution as in dye based inks, are prone to clog the transfer structure as the structure acts as a filter to the suspended pigment particles. This results in undesirable variations in print quality.
The aforementioned prior art devices also have complex structural requirements, are difficult to operate consistently, and do not provide the concise, continuous and uniform metering of ink, particularly ink of the pigmented type, required by scanning operations.
The microporous material of the type described and claimed in co-pending application Ser. No. 7,160 filed Jan. 27, 1987 assigned in part to the same assignee as the present invention is particularly suited to transfer pigmented ink at a constant rate. The material is initially ink impregnated and consistently transfers ink without substantial loss until the ink supply within is essentially depleted. Once depleted, the roll of microporous material is either discarded or impregnated again for subsequent use. At times it is preferable, however, to utilize such a material to its best advantages in continuous and extended use. The ink feed rollers of the prior art, as described above, lack the ability to provide an extended and precise metering of pigmented ink to the material for the detailed and prolonged printing required in some circumstances to permit reliable and extended printing of fast moving substrates with minimal decrease in impression intensity.